1. Field of the Invention
The present invention relates to a display device and method of manufacturing the same, and more particularly, to a polarization control unit that is suitable for a 2D/3D image display device.
2. Discussion of the Related Art
Stereoscopic image displays are categorized into stereoscopic displays and auto-stereoscopic displays. The stereoscopic displays, which use parallax image of the left and right eyes of a viewer with a high stereoscopic effect, include glasses-type displays and glasses-free type displays, both of which have been put to practical use.
In the glasses-type displays, left- and right-eye parallax images are displayed on a direct-view display element or a projector by changing the direction of polarization or in a time-division manner, and polarization glasses or liquid crystal shutter glasses are used to represent a stereoscopic image. The glasses-free type displays are generally classified into parallax barrier displays and lenticular displays.
The parallax barrier displays present stereoscopic images separately to the left and right eyes of the viewer by selectively blocking light incident from the display panel using a barrier. A disadvantage of this technology is that it has significant luminance loss because the light passing through the barrier is reduced by about 50% or less as compared with incident light. The lenticular displays present stereoscopic images separately to the left and right eyes by using al lenticular lens positioned between the display panel and the viewer. The lenticular displays have less luminance loss than the parallax barrier displays.
However, the aforementioned parallax barrier and lenticular displays may be difficult to display 2D images because optical separation cannot be switched on and off. with no or less luminance loss.
The switchable display is a display that switches between 2D and 3D by controlling the voltage applied to the liquid crystals, and includes a display panel for displaying an image, a polarization control unit for representing a 3D image and polarizing lenses. A known switchable polarization control unit is disclosed in International Laid-Open Patent Publication No. WO 2013/077664 entitled “Stereoscopic image display device” andAccordingly, a switchable display has been proposed that is switchable between 2D and 3D, filed on May 30, 2013.
This polarization control unit, referred to as a switchable diffuser in this international laid-open patent publication, includes an upper substrate and a lower substrate with electrodes formed on their opposing surfaces and a polymer-dispersed liquid crystal (PDLC) layer disposed between the upper substrate and the lower substrate. The polymer in the polymer-dispersed liquid crystal layer forms a matrix structure that supports the liquid crystal molecules. The polymer alignment in the liquid crystal layer can be controlled by applying a voltage to the polarization control unit, thereby controlling light scattering and transmission.
However, the upper and lower substrates of this polarization control unit should maintain an appropriate distance from each other to avoid contact. Especially, the retardation uniformity issue associated with the bending and thickness variations of the upper and lower substrates may make it difficult to perform optimum retardation design. Such difficulties in optimizing retardation may cause color diffusion by wavelength and light leakage, leading to lower optical efficiency.
Moreover, if the distance between the upper and lower substrates is too narrow, the upper and lower substrates may be shorted due to substrate bending or external pressure, causing a failure.